The conventional technologies for packaging the semiconductor components are still faced with limitations due to the facts that the packaging processes require longer processing time and higher fabrication costs. The limitations of the conventional technologies can be illustrated by the processes of packaging the semiconductor components as described below.
The first one is sawing method, including following steps: Step 1, Chip attachment. Attach semiconductor chips on pre-platted lead frame with a tape attached on the lead frame back side. The lead frame may comprise of a plurality of lead frame units, with each unit containing a die pad and a plurality of leads. The semiconductor chips are attached onto the die pads for each lead frame unit. Step 2, Wire bonding. For each lead frame unit, use metal wire respectively to connect the chips and leads. Step 3, Encapsulation. Encapsulate the chip, die pad and leads into a plastic-sealed body. Step 4, Tape stripping. Strip the tape at the back of whole lead frame to expose the metal lead portion on the bottom surface of the plastic-sealed body. Step 5, Attach UV tape. Attach an UV tape on the front surface of lead frame encapsulation. Step 6, Sawing process. Saw through the plane of the whole encapsulated lead frame in both horizontal and longitudinal directions to form a plurality of singulated semiconductor components. Step 7, Detach UV tape. Solidify the UV tape by using ultraviolet radiation, and detach the cut encapsulated components from the UV tape.
The above sawing method of semiconductor packaging provides higher density of lead frame unit on a whole lead frame therefore provides the benefit of material saving. However, this semiconductor packaging method has the following technical problems. 1. The sawing process simultaneously saws through the plastic-sealed body and the inner metallic leads resulting in metallic burr and distortion at the tips of the leads or even causing de-lamination between two kinds of material, greatly degrades the quality of semiconductor components. 2. The longer time required to saw along both horizontal and longitudinal directions leads to lower productivity. 3. The semiconductor components packaged by this method are unleaded with the leads encapsulated inside the plastic-sealed body except only a portion of the bottom surface of the leads exposed through the bottom of plastic-sealed body for soldering onto a PCB. The soldering quality may degrade due to smaller lead surface area available for soldering.
The second method is lead punch method, including the following steps. Step 1, Chip attachment. On different lead frame units in lead frame, attach the chips onto its die pads, respectively. Step 2, wire bonding. For each lead frame unit, use metal wire to connect its chip and leads. Step 3, plastic encapsulation. Form separate plastic encapsulation for each lead frame unit. Encapsulate the chip, die pad, and some leads of each individual lead frame unit into discrete plastic encapsulation cavities. In this step, the metallic tie bars on the lead frame are taken as divider, thus forming several plastic encapsulation cavities. The metallic tie bar is used to connect different plastic encapsulation cavities through the corresponding leads connected thereon. Step 4, removal of excessive encapsulation material at the edge of plastic-sealed body. Step 5, plating. Plate a metallic layer on external exposed metallic portion on lead frame. Step 6, tie bar punching and separation. Remove the metallic tie bars between different plastic encapsulation cavities by punching off the connection between leads in each lead frame unit and preserve a desired portion of leads extending outside the encapsulation therefore forms a plurality of separated semiconductor component packaged products with external leads.
If the semiconductor components are plastic encapsulated by the above lead-punching method, the density of lead frame unit arranged on lead frame is low in order to provide extra space for punching, thus resulting in low material utilization factor and waste.
Therefore, it is necessary to provide a new and improved packaging process for semiconductor components with external leads to package the semiconductor components with more convenient processing steps to simplify the manufacturing processes and reduced the production costs such that the above discussed limitations and difficulties can be resolved.